Cavitation is related to formation of bubbles and cavities within a liquid. Bubble formation may result from a localized pressure drop in the liquid. For example, if the local pressure of a liquid decreases below its boiling point, vapor-filled cavities and bubbles may form. As the pressure then increases, vapor condensation may occur in the bubbles and they may collapse, creating large pressure impulses and high temperatures. When cavitation is used for mixing of substances, the process may be called high-shear mixing.
There may be several different methods to produce cavitation bubbles in a liquid. One method may be to rotate a propeller blade in or through the liquid. If a sufficient pressure drop occurs at the blade surface, cavitation bubbles may result. Another method may be to move a fluid through a restriction, such as an orifice plate. If a sufficient pressure drop occurs across the orifice, cavitation bubbles may result. Cavitation bubbles may also be generated in a liquid using ultrasound.
The impulses and high temperatures produced by collapse of cavitation bubbles may be used for various mixing, emulsifying, homogenizing and dispersing processes, and also to initiate and/or facilitate a variety of chemical reactions. Devices and methods designed to produce cavitation in liquids, however, may not sufficiently control either the rate of formation of cavitation bubbles, the collapse of cavitation bubbles, or the location at which they are formed. For example, uncontrolled cavitation in a chemical reaction may result in pressures and/or temperatures that could damage chemical reactants or products. In another example, formation of cavitation bubbles along the surface walls of a cavitation device could cause premature erosion of the surface.